Synchro-mesh type gear transmission

ABSTRACT

A synchro-mesh type gear transmission includes a clutch hub rigidly mounted on an output power shaft. The clutch hub is provided with axial slots in which springs are axially inserted. The springs urge at least one synchronizer ring against a conically tapered surface of a driven shaft gear which is mounted on the output power shaft so as to be rotatable. The synchronizer ring exerts frictional resistance against rotation of the driven shift gear. At least a portion of the inner wall of each guide slot is located in a spline-toothed flange portion of the clutch hub. The inner wall portion of the guide slot which is in the flange portion provides an additional guide for the spring. The spring is thereby prevented from being deformed in the direction in which the synchronizer ring rotates.

BACKGROUND OF THE INVENTION

This invention relates to synchro-mesh type gear transmissions of thetype used in motor vehicles, and more particularly, to a geartransmission provided with means for the reduction of gear backlashnoise.

In engines for motor vehicles, the speed of engine rotation and thecorresponding output torque vary over a large range. Gear-type powertransmissions which are generally used with such engines produceannoying gear backlash noise which cannot be ignored. The gear backlashnoise is not very significant when the engine is running at high speed,because during such operation the rotation speed and torque vary over arelatively small range, while air intake suction noises, and exhaustnoises, are louder than when the engine is rotating at low speed.However, when the vehicle is stopped and the engine is idling, evensmall variations in the actual speed of rotation of the engine arerelatively larger than when the engine is operating at high speed.During such low speed operation, large relative speed differentials mayoccur between an input gear and a counter input gear which is in directengagement with the input gear, thereby, producing relatively loud gearbacklash noise.

The magnitude of gear backlash noise is related to frictionalresistance, which is affected by the viscosity of the lubrication oil.For example, as the temperature of the lublication oil increases, andthe frictional resistance between transmission components decreasesbelow a certain value, gear backlash noise is generated.

An improved synchro-mesh type gear transmission which reduces gearbacklash noise has been proposed in Japanese Utility Model PublicationSho. 53-6755. The transmission described therein is provided with aclutch hub having axial slots in which springs are inserted. The sprinsurge a synchronizer ring against a conically tapered surface of a shiftgear, thereby exerting a frictional resistance against the movement ofthe shift gear. However, in this known gear transmission, no means areprovided for guiding the springs, thereby allowing the springs to bedisadvantageously deformed in the direction in which the synchronizerring rotates.

It is, therefore, an object of the present invention to provide a newand improved synchro-mesh type gear transmission which eliminates thepossibility of undesired spring deformation.

It is another object of the present invention to provide a new andimproved synchro-mesh type gear transmission which includes spring meansfor exerting a frictional resistance by urging a synchronizer ringagainst a driven shift gear, in such a manner that gear backlash noiseis eliminated while the spring means are prevented from beingundesirably deformed.

SUMMARY OF THE INVENTION

The foregoing and other objects are achieved by this invention whichprovides a synchro-mesh type gear transmission having a clutch hubrigidly mounted on an output power shaft, the clutch hub being providedwith axial guide slots in which springs are axially inserted. Thesprings urge a synchronizer ring against a conically tapered surface ofa driven shift gear, which is mounted on the output power shaft so as tobe freely rotatable. Thus, the synchronizer ring exerts a frictionalresistance against the rotation of the driven shift gear. A sleevemember is provided which is in constant meshing engagement with theclutch hub and which selectively engages the desired driven shift gear.At least a portion of the inner wall of each guide slot is on a flangeportion of the clutch hub.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of an embodiment of a geartransmission of the present invention;

FIG. 2 is a partial cross-sectional view of another embodiment of thepresent invention;

FIG. 3 is a partial cross-sectional view of a further embodiment of thepresent invention;

FIG. 4 is a partial cross-sectional view of still another embodiment ofthe present invention;

FIG. 5 is a plan view of a fragmented clutch hub used in a geartransmission of the present invention;

FIG. 6 is a fragmented plan view of another clutch hub used in a geartransmission of the present invention;

FIG. 7 is a cross-sectional view of a synchronizer ring used in a geartransmission of the present invention;

FIG. 8 is a plan view of the synchronizer ring illustrated in FIG. 7;

FIG. 9 is a partial cross-sectional view of a conventionally known geartransmission, and;

FIG. 10 is a cross-sectional view taken along line X--X in FIG. 9.

DETAILED DESCRIPTION OF A PRIOR ART GEAR TRANSMISSION

A synchronizer mechanism of a synchro-mesh type gear transmission (i.e.,a Borg-Warner type gear transmission) is well known from prior art.Thus, a detailed description concerning the construction and operationthereof will not be provided. A gear transmission disclosed in theabove-mentioned Japanese Utility Model Publication No. 53-6755, in whicha frictional resistance is exerted on a driven shift gear by means of aspring, will be briefly described.

In FIGS. 9 and 10, a clutch hub 18 is provided with axially extendingslots 18c which are angularly situated 120° apart and positionedcorresponding to the periphery of a pair of synchronizer rings 16 and17. Each slot 18c contains a compression spring R, the ends of whichcontact respective ones of synchronizer rings 16 and 17. Springs Rsoftly urge rings 16 and 17 against conically tapered surfaces 6b and 7bof gears 6 and 7, respectively. The magnitude of the total springexpansion force of springs R which is applied against synchronizer rings16 and 17 need be only enough to apply a small frictional resistanceagainst gears 6 and 7. Shifting keys 20 are urged radially outward by apluarality of key springs 21'. The spring expansion force of key springs21' must be sufficient to urge synchronizer rings 16 and 17 againstconically tapered surfaces 6b and 7b of gears 6 and 7, respectively, bymeans of shifting keys 20, when the synchronizer mechanism is operated.During such operation, a phase differential is present between therotation of an inner set of spline teeth of a sleeve 19, and therotation of the outer sets of spline teeth of synchronizer rings 16 and17, respectively. The substantially circular key springs 21' havestraight portions 21'b which are radially inwardly deformed, asillustrated in FIG. 10, so as to permit springs R to be disposed inaxial slots 18c, without interference by key springs 21'.

In the neutral position, as shown in FIG. 9, if the vehicle is stopped,an output power shaft 2 is not rotated. However, an input power shaft(not shown in the drawings) is rotated through a main clutch assembly byan engine which is idling. Counter gears (not shown), which are mountedon a counter shaft (not shown) are always rotated by an input gear (notshown) which is rigidly mounted on, or integrally formed with, the inputpower shaft, and shift gears 6 and 7 which are in constant meshingengagement with the counter gears, are always freely rotated on outputpower shaft 2. The synchronizer rings 16 and 17 are softly urged againstconically tapered surfaces 6b and 7b of shift gears 6 and 7,respectively, by means of springs R, so that a frictional resistance isexerted on shift gears 6 and 7. The frictional resistance is transmittedto the counter gears, which are rigidly mounted on the counter shaft andare in constant engagement with shift gears 6 and 7, and is subsequentlytransmitted to the input gear, thereby preventing gear backlash noisefrom being produced when the engine is running in an idling condition inwhich the relative change of speed of rotation, or turning torque, isvery large.

Guide slots 18c, in which springs R are respectively inserted, areaxially formed at the relatively thin flange wall portion of the clutchhub 18, so that the springs R are not fully retained or guided in theslots 18c along the entire axial length of the springs R. Therefore,when a shift lever is manually operated, and a selectable one ofsynchronizer rings 16 and 17 is synchronized with respect to clutch hub18, springs R tend to deform in the direction in which the selectedsynchronizer ring rotates, and thus, the shift operation tends to beneither softly nor smoothly carried out.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 through 4, several embodiments of the presentinvention are illustrated, in which axial guide slots 18c are formed ina clutch hub 18, so that at least a portion of the inner wall 18e ofeach guide slot 18c is in a flange portion 18d (See FIGS. 5 and 6) ofclutch hub 18. Inner wall portion 18e provides an additional guide forspring R. Springs R are thereby guided along their entire axial length,so that when a synchronizer ring is synchronized with clutch hub 18, thesprings are prevented from being deformed in the direction in whichsynchronized synchronizer ring rotates. Accordingly, the amount of forcerequired to be applied by springs R may be small and the shift operationcan be softly and smoothly carried out when a shift lever is manuallyoperated.

In the embodiment illustrated in FIG. 1, guide slots 18c extend axiallythrough clutch hub 18. The ends of each spring R urge respectivesynchronizer rings 16 and 17 against corresponding, conically taperedsurfaces 6a and 7b of shift gears 6 and 7.

In the embodiment illustrated in FIG. 2, guide slots 18c are axiallyformed in clutch hub 18 so that one end of each of the guide slots 18cis opened while the other end thereof is closed. Thus, springs R urgeonly synchronizer ring 17 against the corresponding, conically taperedsurface 7b of shift gear 7.

In the embodiment illustrated in FIG. 3, synchronizer rings 16 and 17have guide recesses 16a and 17a, respectively, at the portions thereofwhere springs R extend. A synchronizer ring, such as 16 or 17, is alsoillustrated in FIGS. 7 and 8. Springs R are retained and guided byrecesses 16a and 17a as well as by guide slots 18c. The dimensions ofrecesses 16a and 17a in the peripheral direction are larger than thecylindrical outer diameter of coil springs R. In view of the increasedguide length which results from guide recesses 16a and 17a, relativelylong springs R, which are easily designed and arranged, must be used.The other aspects of the embodiment illustrated in FIG. 3 are the sameas those of the embodiment illustrated in FIG. 1.

In the embodiment illustrated in FIG. 4, guide slots 18c are axiallyformed in clutch hub 18 so that one end of each of the guide slots 18cis opened while the other end thereof is closed, in a manner similar tothat discussed above with respect to the embodiment illustrated in FIG.2. Synchronizer ring 17 is provided with guide recesses 17a at theportions where springs R extend. This is similar to the embodimentdiscussed above and illustrated in FIG. 3.

If the radial thickness of the externally spline-toothed flange portion18d of clutch hub 18 is relatively small, the portions of flange portion18d near guide slots 18c may be formed without spline teeth as shown inFIG. 6. this will permit the coil diameter of springs R to be largerthan would be permissible with the clutch hub of FIG. 5.

Although the inventive concept disclosed herein has been described interms of specific embodiments and applications, other embodiments andapplications would be obvious to persons skilled in the art in light ofthis teaching, without departing from the scope of the invention. Thedescription and drawings of specific embodiments are illustrative ofapplications of the invention and should not be construed to limit thescope thereof.

What is claimed is:
 1. A synchro-mesh gear transmission of the typehaving a clutch hub which is rigidly mounted on an output power shaft,the clutch hub being provided with axial slots in which springs areaxially inserted, the springs being arranged so as to urge asynchronizer ring against a conically tapered surface of a driven shiftgear, the driven shift gear being mounted on the output power shaft soas to be rotatable with respect to the output power shaft, thesynchronizer ring thereby exerting a frictional resistance againstrotation of the driven shift gear, the driven shift gear beingselectively coupled to the clutch hub by a sleeve member which is inconstant meshing engagement with the clutch hub, the transmission beingfurther characterized in that at least a portion of an inside wall of atleast one guide slot is in a peripheral flange portion of the clutch hubso as to provide support against axially transverse deformation of thespring.
 2. The transmission set forth in claim 1, wherein one end ofsaid guide slot which has at least a portion on an inside wall in saidperipheral flange portion is opened so as to permit the spring tocommunicate with the synchronizer ring, while the other end thereof isclosed.
 3. The transmission set forth in claim 1 or 2, wherein thesynchronizer ring is provided with a guide recess at a predeterminedportion thereof, so that the spring is supported against axiallytransverse deformation by the combination of said guide recess and saidguide slot which has a portion of an inside wall in said peripheralflange portion of the clutch hub.
 4. The transmission set forth in claim1 wherein said peripheral flange portion of the clutch hub has anuntoothed portion on its outer perimeter near said inside wall, of saidguide slot, in said peripheral flange portion.